A DC power supply apparatus of the above-described type may be used for, for example, an arc welder, an arc cutter, a charger and an electroplating apparatus. In some areas, a plurality of AC voltages, e.g. voltages of 100 V and 200 V, or voltages of 200 V and 400 V, may be available, and a DC power supply apparatus may be arranged to operate from any one of such plural AC voltages. An example of DC power supply apparatuses which can operate from either of such different AC voltages includes a voltage-boosting converter. In this power supply apparatus, whatever AC voltage is inputted, the input AC voltage is rectified and voltage-boosted to a voltage having a predetermined value by the voltage-boosting converter. The voltage-boosted voltage is, then, converted to a high-frequency voltage by a high-frequency inverter, which, in turn, is voltage transformed. The resulting transformed high-frequency voltage is rectified and applied to a load.
The above-described DC power supply apparatus includes semiconductor switching devices in the inverter, which are switched at a high frequency. When the switching devices switch, both current and voltage are simultaneously applied to the switching devices, switching loss may occur. In order to reduce such switching loss, the switching frequency cannot be high. It has been only up to about 15 KHz at the highest.
An object of the present invention is to provide a DC power supply apparatus including an inverter that can operate at a high switching frequency with little switching loss and, at the same time, can provide a desired DC voltage from an input AC voltage of any magnitude.